1. Field of the Invention
The present invention relates to internal combustion automobile emissions measurements for which results are to be obtained in the form of mass per distance traveled (or mass per unit of time) for each pollutant of interest rather than as a simple concentration. More particularly the present invention is directed to a method and apparatus that reduces the size and power consumption of the equipment needed for such a measurement to a point where it can be conveniently installed in a moving vehicle for accurate, on-the-road, real-time measurements.
2. The Background
Vehicle gas pollutant mass flow measurements are traditionally made by the Constant Volume Sampling (CVS) method. Traditional CVS equipment dilutes the entire vehicle exhaust flow to a constant volume flow with a variable amount of fresh air, so that the resultant concentration of each pollutant is directly proportional to its mass flow at the tailpipe. The air pumps needed for this method must operate at a flow larger than the greatest expected exhaust flow of the engine under test and, as a result, are too large and need too much power to be conveniently installed in a vehicle such as the vehicle to be tested.
Prior art schemes for reducing the bulk and power consumption of emission mass flow measurement have included the concept of performing the constant volume dilution on a small (fixed) fraction of the total exhaust flow using calibrated orifices, flow restrictors and other fluidic components to perform the needed functions. Such schemes have had the disadvantages of poor accuracy over the broad dynamic range needed for real-time on-the-road passenger vehicle pollution performance evaluation and need hardware changes to rescale the operating exhaust mass flow range for different test conditions or vehicle models.
The U.S. Code of Federal Regulations (CFR) Tide 40, part 86, p. 444, section 86.140-82 entitled "Exhaust Sample Analysis" discusses present requirements for CVS measurements in the United States in connection with measuring automobile exhausts for compliance with environmental regulations. It would be desirable to meet these requirements for CVS measurements in a portable device easily adapted to and carried by any vehicle.